Loudspeaker



May 4, 1943. H; F. oLsON 2,313,517. LOUDSPEAKER y' Filed Jan.- 31, 1940- 2 Sheets-Sheet 1 y??? 'C2 2c :Innen or Hwgzmm Patented May 4, 1943 LOUDSPEAKER Harry F. Olson, Haddon Heights, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application January 31, 1940,. semi No.,316,s14

(ci. 17e-115.5)

l Claims.

This invention relates to loudspeakers, and more particularly to mechanical networks therefor for controlling the high frequency response thereof.

It is quite well known that, in general, in radio and other forms of sound reproducing apparatus, it is often desirable to attenuate the response above a certain high frequency limit. In some cases, it may be desirable to attenuate a certain band, as, for example, 10,000 cycles and over in radio reproduction, to eliminate the adjacent channel beat note. To acccmplishthis, there have been provided electrical networks and lters' in the radio frequency, intermediate frequency, and audio frequency stages,` but such networks and filters are usually quite costly as compared to mechanical filters for certain applications in sound reproduction.

Now, I am aware that attempts have been made' heretofore to provide mechanical filters for attenuating the high frequency response of loudspeakers, as shown, for example. in the patent to Carlisle 2,007,750. However, the filters of the prior art of which I am aware do not provide sufcintly high attenuation for all practical purposes, nor do they have as sharp a cutoii as is frequently desired.

The primary object of my presentinvention is to provide improved mechanical networks for loudspeakers of the dynamicA type by means of which the high frequency response may be controlled satisfactorily over a wide range.

More particularly, it is an object of my present invention to provide an improved band elimination mechanical network for loudspeakers by means of which it is possible to suppress certain frequency bands in the high frequency region, or to attenuate the high frequency respense.

Another object of my' present invention is to provide an improved vibratile system for acoustic apparatus of the dynamic or moving coil type.

,Still another object of my present invention is to provide improved mechanical networks as aforesaid which may be readily applied to existing loudspeakers with great facility.

It is also an object of my present invention to provide improved acoustic apparatus as aforesaid which is extremely simple in construction,

which readily lends itself to rapid quantity production, which is very inexpensive in cost, and which is highly eicient in use.

Inaccordance with my present invention, I provide the loudspeaker with a voice coil form which extends through the cone or diaphragm,

the form carrying the usual voice coil on that portion thereof which extends to one side ol' the diaphragm and having a compliance therein in that portion which extends to the other side of the diaphragm. Preferably, also, a small mass is attached to the end of the voice coil form in which the aforementioned compliance is formed. If desired, the coil form may also be provided vwith one or more compliances in that portion thereof on which the-voice coil is mounted. In any case, a dust cap Imay be secured to A the diaphragm over the end of the voice coil form which carries the mass in order to reduce radiation therefrom. The eiect of adding networks of this type'is the same as introducing into the equivalent electrical circuit of the vibrating systemy one or more parallel resonant networks which have the eect of providing sharp cut-oil and relatively high attenuation at the higherfrequencies.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method. of operation, as well as additional objects and advantages thereof, will best be understood from the following description of several embodiments thereof. when read in connection with the accompanying drawings, in which:

Figure 1 is a view of a. loudspeaker withone form of my invention appliedv thereto.

Figure 2 is the equivalent electrical circuit of the vibrating system shown in Fig. 1,

Figure 3 is a response curve showing the frequency characteristic of the'acoustic system of Fig. l,

Figure 4 shows a loudspeaker system having another form of my invention embodied therein, Figure 5 is a wiring diagrarn of the electrical equivalent of the system of Fig. 4,

Figure 6 is a response curve showing the frequency characteristic of the system of Fig. 4,

Figure 7' shows a loudspeaker system embodying still another form of my present inventiomf Figure 8 is a wiring diagram of an electrical circuit corresponding to the vibrating system of Figure.9 is a response curve showing the frequency characteristic of the system of Fig. 7,A

Figure 10 shows a vibrating system incorporating still another form of my invention,

Figure 11 is a wiring diagram of an electrical 'l trical circuit equivalent to similar to that shown in Fig.

'has the veffect of tively,` l ance of the cone Figure 12 is a response curve showing the frequency characteristic of the system of Fig. 10,

Figure 13 is affragmentary view of a loudspeaker system embodying still another form of my present invention,

Figure 14 is a wiring and Figure 15 is a fragmentary Referring more particularly to the drawings, wherein similar reference numerals indicate corresponding parts throughout, there is shown,Y in

Fig. l, a vibratile member in the form of a cone or diaphragm I to which is secured a voice coil form 3 which extends through the diaphragm. The diaphragm I may be provided with an annular rim or ilangei which 'may be clamped in place between a pair of suitablevrings 1 in well-known manner and it preferably also has secured thereto a'spider 9 for centering the voice coil form3 in the air gap of a suitable magnetic systeminot shown).

The voice coil form 3 has mounted thereon a suitable voice coil II on that portion thereof Preferably, also, a ring I5 is secured to the upper end of the voice coil form 3 beyond the compliance I3 to provide a mass on the form 3.

Fig. 2 lshows the electrical analogue of the system shown in Fig. 1. It willbe noted that the compliance c:l and the resistance r2 of the corrugation I3 and the mass mani the ring I5 form a parallel resonant circuit in series with the mass 'mi of the voice coil II, the compliance cs of the spider 3 and the impedance Ze of the cone I. The driving force ,generated inv the voice coil II is designated as f in the equivalent electrical circuit of Fig. 2. By employing a mechanylcal network of this sort, the coupling between the voice coil. II and the'cone or diaphragm I diagram showing the electhe system of Fig. 13,

I view ofi a modified arrangement of the system shown in Fig. 1.

I lower end'of the voice coil form 3 to provide sistance n where ma is the that, in the system of Fig. l, the attenuation decreases above the resonance frequency of the parallel circuit constituted by mz, cz and n. At about 13,000 cycles and above, there is no attenuation. In most cases, however, It is desirable to attenuate the entire band above 10,000 cycles, and this may be accomplished veryreadily by the system shown in Fig. 4 wherein the compliance I1 is inserted between the voice coil II and the cone I. The response curve of Fig. 6 shows that there is considerably more attenuation at 10,000 cycles and above 10.000 cycles in the system of Fig. 4 than there is in the systemof Fig. 1.

In Fig. 7, I have shown still another niodication of my invention which embodies a, single section filter connecting the voice coil mass mi and the cone impedance Za as clearly shown in Fig. 8. This is accomplished by providing an additional corrugation or compliance Il on the the additional parallel resonant circuitlcorresponding to the mass ma, compliance ca and remass of the added portion, or lower end, of the voice coil form 3 below the compliance I3, and c: andn are,

will be reduced at the resonant frequency of the parallel circuit provided by the mass ma, the compliance cz and theresistance rz. The frequency response characteristic of this system is shown in Fig. 3 from which it will be seen that the response is attenuated about 20 db. at about 10,000 cycles.` The attentuation at resonance of the aforementioned parallel circuit is governed by the resistance in the compliance I3. 'I'he sys'- tem just described can be-easily fabricated by simply making is 'customary in conventional loudspeakers and rolling in an appropriate corrugation or compliance I3. The width of the attenuation band is, of course, governed by the constants of the system. L V

In Fig. 4 I have showna system which is quite Y 1 but wherein the voice coil form 3 is made somewhat longer and an additional compliance or corrugation provided therein adjacent the .voice coil II. This shunting the vseries connected compliance ci and theresistance 1'1, which correspond to thecompliance and resistance, respecof the corrugation I1, across the imped- I, as clearly shown in Fig. 5.' -From an 'inspection of Fig. 3, it will be noted respectively, the compliance and resistance of g the corrugation I9. Since the impedance of the spider s is very small, it may be neglected, and the system is. therefore effectively a T type low pass iter connecting the voice coil II and the cone I. Very high attenuation may be obtained at the resonance frequency of the two arms of the lter, as represented by the two parallel resonant circuits. The response frequency characteristic of this modification of my invention is shown in Fig. 9, from which itwill be noted that, at 10,000 cycles, the attenuation is about 35 db., being also quite high above 10,000 cycles. As in the systems previously described, the additional corrugation I3 may be formed very easily by simply rolling itinto the voice coil form 3 along withthe corrugations I3 and I1 to provide a single voice'coil form having the plurality of corrugations.

Fig. 10 shows a system similar to that of Fig. 'I but wherein. the cone I is also provided witha corrugation or other suitable compliance 2| adjacent its connection to the voice coil form 3. -If

` its resistance r4, and the mass of that part of the voicecoil form 3 longer than the coil form 3 between the corrugstions I3 and I1 plus the mass of the part of the cone I between the corrugations I1 and 2l is m4, the equivalent electrical circuit of this system will be as shownin Fig. 11 with the capacitance `c4 and resistance n shunted across the impedance Ze,

retaining the T type lter which connects the voice co 'mass ,m1 and the cone impedance Ze,

as in Fig. 8. The response curve of Fig. 12 shows that, at 10,000 cycles, the attenuation of the sys-4 tem of Fig. 10 is about the same as that of Fig. '1, but above 10,000 cycles about 4 db. more attenuation is obtained with the system of Fig. 10 than with the system of Fig. 7.,

In Fig. 13, I have shown still another modiilcation of-niy linvention which is similar to thst'of Fig. 10 but provide an additional form 23. which is secured tothe cone or diaphragm I concentrlcally with the voice coil form 3 and on the other side of the corrugation or 'compliance 2I. This provides a two-section filter, as

clearly shown in Fig. 14, wherein the mass 1m corresponds to themass of the form I3, the'compliance c and the resistance r5-correspond, respectively, to the compliance and resistance of the corrugation 25, and me corresponds to the mass ofthose portions of the form 23 and the cone I which are between the corrugations 2| and 25.

With suitably chosen constants for thesystem of Fig. 13, it is possible to obtain an attenuaof 4the various masses under certain conditions of operation and design. In order to reduce this vibration to a-minimum value, a dust cap 21 may be added to the system by securing it to the cone I over the upper end of the voice coil form 3, as clearly shown in Fig. 15;

From the foregoing description, it will be apparent to those skilled in the art that I have provided several novel band elimination mechanical networks for loudspeakers for suppressing theV response thereof at 10,000 cycles as well as the adjacent" channel beat notes. 'All of the networks described ean be built at an extremely low cost and may be easily incorporated in dynamic loudspeakers of otherwise conventional design. Although I have shown and described a number of embodiments of my invention, it will be apparent to those skilled in the art that many` changes in the modifications described, as well as many additional embodiments thereof, are possible. Forlexample, instead of using a voice coil as the driving'element for the cone' |,.any other suitable driver may be used, such as a. crystal unit, a magnetic motor, a condenser unit, or any other similar driver, in which case the coupling member between the driver and the cone l could be made to extend through the cone and be provided with one or more corrugations similarly to the Voice coil form herein described. In fact, wherever I have used the term voice coil form throughout the preceding description and in the appended claims, I

intend this to include also any form of cou-v pling means between the. diaphragm or vibraat the end thereofbeyond said compliance providlng a mass therefor.

3. Acoustic apparatus comprising, in combination, a vibratile member. a voice coll form secured thereto and extending through said member with its ends freely suspended for vibration with said member, and a. voice coil carried by said form, saidform .having a plurality of compliances therein, at least one of said compllances being on that portion of said form which extends to one side of saidmember and at least one other of said'compliances being on that portion of said form which extends to the other side of said member. l

4. The invention set forth in claim 3 characterized by the addition of a mass at one end of said form beyond the compliance on that portion of said form ter nating in said one end.

5. Acoustic apparatus comprising, in combination, a vibratile member, a voice coil form' secured thereto and extending' through said member with its ends freely suspended for vibration with said member, a voice coil carried by said form on the portion thereof extending to one side of said member,'said pory tionhaving at least one compliance therein, and a compliance in the portion of said lform ex-' tending to the,other side of said member.

6. Acoustic apparatus comprising, in combination, a vibratile member, a voice coil form secured theretoand extending through said member with its ends freely suspended for vibration with said member, a voice coil carried by said form on the vportion thereof extending to one side of said member said portion having a plurality of compliances therein in spaced relation along its length and vsaid voice coil lying between an adjacent pair'of said compliances, the mass of that, part of said voice coil form which lies beyond that one of said pair of compliances which is most remote from said vibratile member cooperating with said last named compliance to form therewith a resonant network, and a compliance in 'the portion of said form extending to the other` side of 7. Acoustic apparatus comprising, in combination, a vibratile member, a voice coil form securedthereto and extending through said mem ber with its ends freely suspended for vibra;

tion with said member, a voice coil carried by tile member and the driving unit therefor' of whatever nature. Accordingly, I desire it to be understood that I do not wish to be limited except insofar as is made necessary by the prior art and the .spirit of the appended claims.

I claim asmy invention:

1. Acoustic apparatus comprising, in combi-' nation, a vibratile member, a voice coil form secured thereto, said form extending through said member with at least one of its ends freely suspended for vibration with said member, a

voice coil carried by said form onl one side of said member, and a compliance in said form on 'the other side of said member.

2. Acoustic apparatus comprising, in combination, a vibratile member, avoice .coil form secured thereto, said form extending through said member with, its ends freely suspended for. vibration with said member, a voice coil carried by said form on one side of said member, a compliance in said form on the other sidel of `said member, and means carried bysaid form said form on the portion thereof extending-to one side of said member, said portion having a plurality of -compliances therein in spaced relation .along its length and said voice coil lying between an adjacent pair of said compliances,

,the mass of that part of said voice coil form which lies beyond that one/of said pair of compliances which is most remote from said vibratile member cooperating with'said last named compliance to form therewith a resonantnetwork, a compliance in the portion of said form extending to the other side of said diaphragm, and a. mass secured to the last named portion of .said form at the 'end thereof beyond said last named compliance.

8. Acoustic apparatus comprising, in combination, a vibratile member, a. voice coil form secured to said member and extending through said member with its ends freely suspended for yibration withsaid member, and a voice coil carried by said -form on the portion thereof extending to one side of said member, said form having a 'compliance in the portion thereof extending to the other side of said member, and

form which lies said diaphragm also having a compliance theref in adjacent its connection to said form.

- 9. The invention set forth 1n claim s char;

nally spaced compliances, and characterized further in that said voice coil is carried on said form between said last named pair of compliances, the mass of that part of said voice coil beyond that one o! said pair of compliancesv which is lmost remote from said l secured thereto 12. Acoustic apparatus comprising, in combination, a vibratile member, a voice coil form and extending :through said member, a 'voice coil carried by said form vibratile member cooperating with said last 'named compliance to form therewith a resonant network.

10. The invention set forth inA claim 8 characterized in that vsaid first named portion of' said form is provided with a pair of longitudinally spaced compliances, characterized further in that said voice coil is carried on said form 'between saidlast named pair of compliances, the mass of that part of said voice vcoil form which lies beyond that one of said pair of compliances which is most bratile member` cooperating with said last named compliance to .form therewith a resonant network, and characterized still further by the addition of a mass on the end of the second named portion of said form.

11. Acoustic apparatus comprising, in combination, a. vibratile member, a voice/coil form secured thereto-and extending through said member, a voice coil carried by said form, said form having at least one compliance, therein on that portion thereof which extendsl said member and at least'one other compliance therein on that portion thereof which extendsv to thel other`side of said member, and asecond form secured to said member in concentric relation to said voice coil form and onthat side of said member which is remote from said voice coil, said second form also having a compliance formed therein. Y

to one side of,

remote from said v iv of said compliances being nation, therefor located to one on the portion thereof extending t0 one side of' said member, compliance in the portion thereof extending to 'the other side of said member, means on the end of said last named portion providing a mass thereon, and a cap secured to said member over said last named portion of said form 'for reducing radiation from said means.

13. Acoustic apparatus comprising, in combination, a vibratile member, a driving element therefor, and means coupling 'said element to said member, said coupling means` extending through said member and having at least one of its ends freely suspended for vibration with said member, said coupling means also having a plurality of compliances therein, at least one of said compliances being formed in that portion of said coupling means which extends to one side of said member and at least one other formed in that portion of said coupling means whichextends to the other side of. said member.

14. Acoustic apparatus comprising, ,in combia vibratile member, a driving element side of said member, and means coupling said element to said member and extending through saidI member beyond the other side thereof,saldmeans having a comv pliance therein in its extension beyond said other side and the end of said extension being freely supported for vibration with said member.

ly supported end oi said extension.

l HARRY F. OLSQEN. l

said form having a 15. The invention set rdm; in c1aim 14 chap, acterized by the addition of a mass on said free-L 

